Microchip has a 2.4Ghz ZigBee compatible SMT radio transceiver module (already FCC certified) that is ~$10 each. Looks like a SPI interface.
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en535967
Seems like a very good alternative to the more expensive XBee and Nordic modules. Has anybody interfaced these with an Arduino yet?
Thanks!